There are many ways of straightening your teeth. Some are free on the NHS for younger people, such as metal braces. Others might be fitted later in life, such as Invisalign, which are fitted retainers that straighten your teeth gradually. They are usually fitted by an orthodontist for older patients who want to straighten their teeth in a subtle way.
The fact that Invisalign is so subtle means it will straighten teeth more gradually over a longer period of time. This is the main reason why people choose it though – it is barely visible when someone is wearing it. The plastic braces are see-through and are changed regularly – a full set of braces is made at the beginning of the treatment. These are then changed over periodically and once the course is complete, teeth should be straight and any difficulties with bite corrected. If more braces are needed they should be made on the treatment plan.